Parallel Universes - The Multiverse
I would explain the theory of Multiverse in three parts. The part one I am going to describe those Nobel prize winning results and highlight a profound mystery which those results revealed.
In part two, I will offer a solution to that mystery is based on approach called string theory and that's where the idea of multiverse come into the story.
Finally in part 3, I am going to describe a cosmological theory called inflation which will pull all the pieces of the story together.
Part 1 - Noble prize winning results
Starts back in 1929, when the great astronomer Edwin Hubble realized that all distant galaxies are rushing away from us establishing that space itself is stretching, it's expanding. Now this was revolutionary, the prevailing wisdom was that on the largest of scales the universe was static.
But even so there was one thing that everyone was certain of. The expansion must be slowing down that as much as the gravitational pull of the earth slows down the ascent of an apple tossed upward. The gravitational pull of each galaxy on every other must be showing the expansion of space.
Now let's fast forward to the 1990s. When the teams of astronomers was inspired by the above reasoning to measure the rate at which the expansion has been slowing. They did this by painstaking observation of numerous distant galaxies allowing them to chart how the expansion rate has changed over time.
Here's the surprise, they found that the expansion is not slowing instead they found that it's speeding up going faster and faster, that's like tossing an apple upward and it goes up faster and faster. So question arises that why, what's pushing on it? Similarly the astronauts results surely well deserving of the Nobel prize, but they raised an analogous question.What force is driving all galaxies to rush away from each other at an ever quickening speed.
Well the most promising answer comes from an old idea of Einsteins. You see we are all used to gravity being that does one thing pulls objects together. But in Einstein's theory of relativity gravity can also push things apart.
How, well according to Einstein Math, if space is uniformly filled with an invisible energy sort of like a uniform invisible mist. Then the gravity generated by that mist would be repulsive gravity. Which is just what we need to explain.The observations because they are repulsive gravity of an invisible energy in space, we now call it dark energy.
It's repulsive gravity would cause each galaxy to push against every other drive the expansion o speed up not slow down and this explanation represents great progress.
Part 2 - String theory
I will tell you three things about string theory. First off, what is it? Well it's an approach to realize Einstein's dream of a unified theory of a single overarching framework that would be able to describe all the forces at work in the universe.
The central idea of string theory is quite straightforward it says that, if you examine any piece of matter ever more finely. At first, you will find molecules and then you will find atoms and subatomic particles. But the theory says that if you can probe smaller much more than we can with existing technology, you would find something else inside these particles, little tiny vibrating filaments of energy a little tiny vibrating string.
Just like strings in a violin, they can vibrate in different patterns producing different musical notes. This little fundamental strings, when they vibrate in different patterns they produce different kinds of particles.
So electrons, quarks, neutrinos, photons all other particles will be united into a single framework and they will all arise from vibrating strings.
Years of research have shown that the math of string theory doesn't quite work. It has internal inconsistencies unless we allow for something wholly unfamiliar extra dimensions of space.
That is we all know about the usual three dimensions of space and you can think about those as height, width and depth. But string theory says that on fantastically small scales there are additional dimensions crumpled to a tiny size. So small that we have not detected them but even though the dimensions are hidden they would have impact on things that we observe because the shape of the extra dimensions constrains how the string can vibrate.
In the sting theory vibration determine everything. So particles masses the strengths of forces and most importantly the amount of dark energy would be determined by the shape of the extra dimension. So if we knew the shape of extra dimensions, we should be able to calculate these features. It means calculate the amount of dark energy.
May be each of this shapes is on equal footing with every other each is a real as every other in the sense that there are many universes each with a different shape for the extra dimensions.
Part 3 - Cosmology
A mechanism has been found by cosmologists trying to understand the Big Bang. You see when we speak of Big Bang, we often have an image of a kind of cosmic explosion that created our universe and set space rushing outward but there's a little secret.
The Big Bang leaves out pretty important. The 'bang' it tell us how the universe evolved after the bang but gives us no insight into what would have powered the bang itself. This gap was finally filled by an enhanced version of the Big Bang's it's called inflationary cosmology.
Which identified a particular kind of fuel that would generate an outward rush of space. The fuel is based on something called a quantum field but only detail that matter for us is that, this fuel proves to be so efficient that it's virtually impossible to use it all up.
Which means in a inflationary theory the big bang giving rise to our universe is likely not a one time event. Instead the fuel not only generate our big bang but it would generate countless other big bangs. Each giving rise to its own separate with our own universe.
Now if we meld this with string theory. Each of these universes has extra dimensions, the extra dimensions take on a wide variety of different shapes, the different shapes yield different physical features and we find ourself in one universe instead of another simply. Because it's only in our universe, that the physical features like the amount of dark energy are right for our form of life to take hold.
How could we confirm the existence of parallel universes?
Well let me describe one way that might one day happen. The inflationary theory has strong observational supports. Because the theory predicts that the big bang would have been so intense that as space rapidly expanded tiny quantum jitters from the micro world would have been stretched out to the macro world.
Yielding a distinctive fingerprint a pattern of slightly hotter spots and slightly colder spots across space. Which powerful telescopes have now observed going further. If there are other universes the theory predicts it every so often those universes can collide.
If our universe got hit by another universe that collision would generate an additional subtle pattern of temperature variations across space that we might one day be able to detect
